I have a chance to pick up a 401 Nailhead to put in the '51 Merc. I know only a little about these engines. Can anyone offer some advice on what to do, and more importantly, what NOT to do? Any advice on intakes? Transmissions? Thanks
I learned after buying a 1960 Buick engine/trans that this was the last year of "closed" drive lines so if you want to use a Turbo 350 trans and "open" driveshaft with the pre-1961 engines you need a pricey adaptor.
If you want to run a non-dynaflow POS trans, then you will need either an adapter OR a '64 ST400 transmission, which are getting hard to find. The nailhead is a great engine, but they are a little goofy when it comes to parts swapping and there is not much in terms of aftermarket parts. There are intakes and such. www.centervilleautorepair.com is the place to find all the performance and adapter goodies. The guy that runs it, Russell Martin is a Nailhead expert.
It's a great motor, rebuilt mine 10 years ago and not one problem with her. Great motors but on the expensive side for performance mods.
Don't let anyone ever tell you to do hardened valve seats. And really a search would have gotten you a lot of really good info... Nope you need a transmission from a 64-66 Nailhead equipped Buick, a bushing and a little work. Pretty easy really. Actually 64 is a one year only valve body, you are better off with a 65-66. And they're really not hard to find if you knwo where to look. Like I've posted before... A source for TH400 trannys: wanted to give everyone a heads up on a good place to look for TH400 transmissions. keep an eye out for jeep pick-ups and wagoneers 1965 to 1972. they have the same bell housing as a 401 nailhead and are th400's. you can unbolt the transfer case adapter and bolt on a 4" tailhousing and your ready to go! the holander number is # 1331, so start looking. i had never seen one till today and stumbled across one. Also Rolls and Bentley you are correct about this trans bolting up to a nailhead, but the output shaft should be a course spline on the jeep & about 3.75" longer than a 2x2. Dave the one i found was out of a 1970 jeep p/u but the output shaft is the same length and spline as my 65 buick trans st400 i have! what do you think the deal is with that! maybe it was changed or something. Yea, sounds like someone changed the shaft to be able to use a later GM transfer case. Good deal for you tho. Just checked on the jeep cores I have & they both have the long course spline output shafts. But you will want to overhaul it anyway, so thats the time to switch shafts.I got tons of the 2x2 shafts if you need some. Dave Most of the nailhead cases in Jeeps have the fine spline short shaft used with the 4" extension housing for Buicks. the exception being the Quadratrac transfer cases. You can also find them in CJ7's until 1980. Even stranger, the Jeeps with a 350 Buick in them used the Nailhead case, with an adapter to bolt to the 350. this is the adapter that might be reversed and used to fit a BOP stick housing to a nailhead. Don't know that it would work, never tried it, May be impossible, I really don't know. The guts will interchange from any T400 to any other T400 case. there are differences. The Buick valve body will hold the trans in the gear selected, and not "blow" shift like a chevy T400.The ST400 parts will fit too, with qualifications. you have to use the ST pump with the ST convertor, and the is an orfice plug that has to go in an oil passage behind the pump at the top of the case. Also, you can use a ST 300 convertor in a ST 400 to get more stall out of the trans. The ST 400 convertor is 13", the ST 300 convertor is 11"
Thanks guys. I did a search as Zman suggested. Found lots of great info including a list of Nailhead shops and service. Still trying to figure out what would be a good intake. I'm wondering if the more wild stuff like dual quads or 6x2 would require a cam swap as well. I'm thinking about 3x2 as well.
Yep..."search" is our friend. There's a ton of great Nailhead threads...where to go, and where not togo!
dual quads run fine with the stock cams. though a little hotter one doesn't hurt. And dual quads make power.
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